1. Related Technical Fields
Related technical fields include altitude reliability determining systems that determine a reliability of a predicted altitude calculated based on road information and altitude information, as well as data maintenance systems and driving assistance systems using the altitude reliability determining systems. In addition, related technical fields include altitude reliability determining programs and methods that determine a reliability of a predicted altitude calculated based on road information and altitude information.
2. Related Art
Driving assistance systems are known, which are configured to determine control property of a vehicle and provide a driver with future information of the vehicle according to altitudes of road surface at a plurality of points on a road. For example, the system disclosed by Japanese Patent Application; Publication No. JP-A-2004-037141 is configured to be able to calculate a predicted altitude based on altitude information (mesh altitude data) provided from the Geographical Survey Institute and road information stored in a map database and execute various kinds of driving assistance processes according to the calculated predicted altitude. In the system of Japanese Patent Application; Publication No. JP-A-2004-037141, in view of the fact that it is difficult to accurately predict road surface altitudes for roads inside tunnels and the like, weighting of predicted altitudes at such points are decreased when calculating interpolating altitude values based on the predicted altitudes at a plurality of points.
Altitude information provided from the Geographical Survey Institute is created based on image information acquired by aerial photographing. Therefore, there are cases, in which an actual altitude (a real altitude) of ground surface differ from the altitude included in the altitude information, depending on the environment in the vicinity of the road even outside a tunnel. For example, in a wooded area, the altitude included in the altitude information may be the altitude of trees instead of the real altitude. The system of the Japanese Patent Application; Publication No. JP-A-2004-037141 does not consider such fact at all. Therefore, the reliabilities of predicted altitudes are not evaluated properly for roads constructed in a wood area. As a result, for roads constructed in areas belonging to specific attributes such as forest zones, the predicted altitudes cannot be calculated with high accuracy. Therefore, there have been cases in which a driving assistance process cannot be executed appropriately.